I have a very powerful Combee, 14'x7' airboat with a 500 cu. in. bored to 519 Cadillac 8 cyl. engine with a 4 barrel Edelbrock carb. in very good condition. The engine does not make a complete revolution before it starts with an HEI ignition. My GPS records the boat at 49 mph in good nautical conditions. Parts for this engine are readily available from all parts stores. (not like the crazy airplane engines used in so many airboats). ( I will provide a new, in the box, water pump as well as a new electric fuel pump.) This engine is mounted on factory pipes and I added 4 schedule 40 stainless steel 2.25" diameter pipes for extra strength and safety. See one in the photo. The fuel tank is a 30 gallon ethylene tank. This engine runs on regular gasoline. See full description on BoatsFSBO.com,.Call Dennis at 410-641-2519 with any questions.